Alternating disturbances that are imparted to a structure frequently cause the structure vibrate. These disturbances can be internal to the structure. For example, when a gun is fired, the alternating explosions of the bullets within the gun cause the gun to vibrate. The alternating disturbances can also be external to the structure. For example, in military situations the firing action of a gun generates and transmits vibrations to the supporting structure of the gun. The gun supporting structure in turn transmits the generated vibrations through its connecting points to a turret connected to the main structure of a vehicle (e.g., helicopter, airplane, ground vehicle, etc.). The turret transmits the vibrations to the main structure of the vehicle. The transmitted vibrations often damage onboard electronics and increase crew fatigue. In another example, a rotating element of a machine can cause the machine to vibrate. This vibration can be transmitted to structures to which the rotating machine is attached. Vibrations generated by rotating machines should be isolated from the main structure or floor on which the rotating machine rests.
Vibration is typically undesirable. Vibration often results in excessive audible noise that gives rise to safety issues, causes fatigue in mounting structures, and the like. Because of the undesirable effects of vibration, numerous methods have been employed in mounts for gun turrets, rotating machinery, or the like to manage vibration. These methods include both passive and active methods. Passive methods usually involve placing a vibration isolator, absorber, or damper between a vibration source, e.g., gun, rotating machine, or the like, and the structure in which the vibration is undesirable, e.g., helicopter shell, rotating machine mount, or the like. Vibration isolators intercept the vibration energy from the vibration source and prevent it from being transmitted to the structure. Vibration absorbers absorb the energy from the source. Vibration isolators and absorbers can be tuned only to one or a few resonant frequencies and therefore are only effective within a narrow frequency band around the selected frequencies. In some instances, vibration isolators and absorbers can amplify undesired vibrations at certain frequencies. Moreover, vibration isolators are not effective for isolating severe shocks or extreme vibratory loads. Vibration dampers receive vibration energy from the source and dissipate it at a faster rate. Dampers add weight to systems, and their performance is temperature dependent and is limited to near-resonant frequencies.
Many commercial and military applications include vibrations over a broad range of frequencies, rendering the above-mentioned passive vibration control methods ineffective for these applications.
Active vibration control methods include feedback and feed-forward vibration cancellation. Feedback vibration cancellation includes measuring the vibration, feeding the measurement back to a controller, sending a control signal from the controller to an actuator, and using the actuator to apply a force or a moment to counteract the vibration. Feed-forward vibration cancellation includes measuring the vibration, feeding the measurement forward to a controller, sending a control signal from the controller to an actuator, and using the actuator to apply a vibration that is substantially identical to the source vibration, with an appropriate phase shift, at or near the source. These active vibration control methods are expensive and hard to implement. Moreover, these methods require excessive amounts of power in that they are applied globally to all parts of the system and therefore are applied to parts of the system that are irrelevant to system performance.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for mounts that include continuous structural elements with vibration energy managing features, that have broader frequency ranges, that are easy to implement, and that can be applied to only those structural areas where vibration control is critical to system performance and therefore are more power efficient.